Freeze-thaw Effect Research Articles

Effects of Freeze–Thaw Cycles on the Mechanical Properties and Microstructure of a Dispersed Soil

Dispersed soil is highly sensitive to water and can easily disperse in low-salt water, leading to weakened structures and engineering issues. To investigate the freeze–thaw effects on the mechanical properties and microstructure of dispersed soils in western Jilin Province, we simulated 0, 1, 3, 5, 7, 9, 12, and 15 freeze–thaw cycles. Qualitative and quantitative analyses were performed using numerous methods, including soluble salt determination, density and water content determination, particle size analysis, dispersion identification tests, and scanning electron microscopy (SEM), to investigate the mechanism of deterioration in soil mechanical properties from various perspectives. The research findings indicate that the unconfined compressive strength (UCS) decreased from 156.843 kPa in the unfrozen state to 76.961 kPa and then stabilized. The freeze–thaw action resulted in particle fragmentation, increased soil porosity, and elevated crack content, thereby contributing to soil structure deterioration and strength reduction. Furthermore, the cohesion value (c-value) gradually decreased from 22.196 kPa in the unfrozen state to 7.997 kPa and then stabilized. The angle of internal friction (φ-value) started at 7.514°, peaked at 9.514°, and gradually declined. This comprehensive study provides valuable insights into the variations in soil mechanical properties under freeze–thaw cycles from multiple perspectives.

Experimental Study on the Effect of Freeze-Thaw Cycles on the Mechanical and Permeability Characteristics of Coal

The safe and efficient mining of coal seams with low porosity, low permeability, and high heterogeneity under complex geological conditions is a major challenge, with the permeability of coal seams playing a crucial role in coal mine gas extraction. The development of coal seam permeability enhancement technology can help coal mines produce safely and efficiently, while the extracted coal bed methane can be utilized as green energy. To study the effect of freezing and thawing on the evolution of the mechanical and permeability properties of coal, triaxial permeability tests were conducted on low-permeability coal under two different confining pressures. Simultaneously, dry, saturated, and freeze-thaw coal samples were set up for comparison, and the effects of water and freeze-thaw were isolated from each other. The triaxial mechanics and percolation laws of dry, saturated, and freeze-thaw coal rocks were obtained; the results show that saturated coal has the lowest initial permeability, while freeze-thawed coal has the highest initial permeability. Through analyzing the effects produced by water, freezing and thawing on coal specimens, the mechanism of the influence of freeze-thaw on the permeability evolution of coal was revealed. The research results can provide theoretical guidance for the development of gas extraction technology for low-permeability coal seams.

Accumulative plastic strain of freezing–thawing subgrade clay under cyclic loading and its particle swarm optimisation–back-propagation-based prediction model

Accurate evaluation of cumulative plastic strains in subgrade soil is crucial for road designs and maintenance. Roads in seasonally frozen regions undergo several freeze–thaw (F–T) cycles annually, resulting in considerable deterioration of soil properties. Under the repeated cyclic loading of moving vehicles, distinct residual deformation occurs in the thawed subgrade. To study the influence of F–T cycles on the cumulative strain characteristics, cyclic triaxial tests were conducted on subgrade clay under the most unfavourable conditions and in situ measured dynamic stress amplitudes. The test results revealed that the cumulative strain (εap) increased with the dynamic stress amplitude. When the dynamic stress amplitude increased from 46 kPa to 70 kPa, εap of unfrozen and F-T specimens increased by more than 14 and five times, respectively. The axial deformation of clay is sensitive to the number of F–T cycles. The freeze-thaw effect was greatest in the first cycle, with εap increasing from 1.42% to 5.63% at the end of the test (dynamic stress amplitude of 46 kPa). In subsequent cycles, relatively small deformations accumulated. A particle swarm optimisation–back-propagation-based (PSO-BP) model for predicting the accumulative plastic strain of clay was developed based on experimental results. In this model, the influences of the F–T process and loading cycles were considered. The prediction performance of the proposed model was validated and compared with that of traditional regression models. The predictions were in good agreement with the experimental data and satisfied the deterioration law for clays subjected to F–T cycles. The maximum error of the PSO–BP model was 2.75%.

Hydraulic conductivity of fine-grained soils subjected to freeze-thaw cycles

This paper presents laboratory data from tests on four fine-grained soils: reconstituted Kaolinite, destructured Bothkennar clay, reconstituted Bothkennar clay, and reconstituted Gault clay. The soil samples were conditioned in an oedometer cell while being subjected to varying numbers of freezing and thawing cycles. The influence of freeze-thaw cycles on key soil parameters, including the hydraulic conductivity, Atterberg limits, compression and swelling index was studied. The experimental results were then compared with the analysis of a previously published database of hydraulic conductivity measurements on fine-grained soils called FG/KSAT-1358. The paper demonstrates that while multiple cycles of freezing and thawing affect some of the studied soil parameters, such as the Atterberg limits and the compression characteristics, the effects on the hydraulic conductivity transformation model parameters, linking the water content ratio to hydraulic conductivity are less apparent. The results are useful for geotechnical and pavement engineers when making assessments of freeze-thaw effects on subgrade materials in cold regions.

Fatigue Property Evaluation of Sustainable Porous Concrete Modified by Recycled Ground Tire Rubber/Silica Fume under Freeze-Thaw Cycles

As an environmentally friendly pavement material, porous concrete in seasonal frozen region is often subjected to repeated loads and freeze-thaw cycles. Therefore, the fatigue property of porous concrete under freeze-thaw is extremely important. However, few researches have been reported on the topic. Based on this background, this paper investigates the flexural fatigue property of ground tire rubber/silica fume composite modified porous concrete (GTR/SF-PC) with experimental and mathematical statistical methods. The flexural fatigue life of GTR/SF-PC under different freeze-thaw cycles (0, 15, 30) was tested with three-point flexural fatigue experiment at four stress levels (0.70, 0.75, 0.80, 0.85). Kaplan Meier survival analysis and Weibull model were adopted to analyze and characterize the flexural fatigue life. The fatigue life equations of GTR/SF-PC under different freeze-thaw cycles were established. The results indicate that, duo to the addition of ground tire rubber and silica fume, the static flexural strength of GTR/SF-PC is not significantly affected by freeze-thaw cycles. The flexural fatigue property of GTR/SF-PC is gradually deteriorated under the action of freeze-thaw cycles. Compared with 0 freeze-thaw cycles, the average flexural fatigue life of GTR/SF-PC decreases about 15% and the fatigue failure rate increases about 50% after 30 freeze-thaw cycles, respectively. The fatigue equations with different reliabilities of GTR/SF-PC show that the reliability is inversely proportional to fatigue life, therefore, the appropriate fatigue equation considering freeze-thaw effect is necessary for fatigue design of porous concrete.

Spatiotemporal Variation in Saline Soil Properties in the Seasonal Frozen Area of Northeast China: A Case Study in Western Jilin Province

Due to the impact of climate change and human activities, the problem of soil salinization is increasingly prominent, posing a threat to the safety of the ecological environment and engineering construction. To understand the development tendency of soil salinization, this paper took the saline soil in Western Jilin province as the research object and carried out a long–term investigation into the basic properties of the soil at several monitoring stations. The results showed that the properties of saline soil in Western Jilin province changed regularly at the spatial and temporal scales. In the longitudinal profile, the water content, soluble salt content, and organic matter content in the soil vary greatly with the seasons at a depth range of 0–50 cm, while their changes below 50 cm are not significant. This is related to the influence depth of the external environment. Meanwhile, the content of sand is relatively stable in the depth direction, mostly between 5 and 15%, while the content of silt and clay fluctuates greatly, and there seems to be a mirror relationship between them. Along the N(W)–S(E) direction, the crystallization proportion of clay minerals gradually increases by about 28% because the relatively humid and hot climate is conducive to mineral crystallization. Over time, in the S(E) study area, the precipitation is relatively abundant, and the shallow soil is desalted due to leaching, resulting in high salt storage in the deep soil. However, in the N(W) study area, salt migrates upwards with water under the dominant effects of evaporation and freeze-thaw, leading to the accumulation of salt in shallow soil and a decrease in salt storage in deep soil. In addition, the saline soil in the study area has strong alkalinity, and the pH increases from 8.2 to 9.8 in the N(W)–S(E) direction. Overall, the soil salinization situation in Western Jilin is not optimistic.

Effect of Composition and Freeze-Thaw on the Network Structure, Porosity and Mechanical Properties of Polyvinyl-Alcohol/Chitosan Hydrogels.

We report the synthesis and characterization of poly (vinyl alcohol) (PVA)/Chitosan (CT) cryogels for applications involving the uptake and entrapment of particulate and bacterial colonies. In particular, we systematically investigated the network and pore structures of the gels as a function of CT content and for different freeze-thaw times, combining Small Angle X-Ray Scattering (SAXS), Scanning Electron Microscopy (SEM), and confocal microscopy. The nanoscale analysis obtained from SAXS shows that while the characteristic correlation length of the network is poorly affected by composition and freeze-thaw time, the characteristic size of heterogeneities associated with PVA crystallites decreases with CT content. SEM investigation evidences a transition to a more homogeneous network structure induced by the incorporation of CT that progressively builds a secondary network around the one formed by PVA. A detailed analysis of confocal microscopy image stacks allows to characterize the 3D porosity of the samples, revealing a significantly asymmetric shape of the pores. While the average volume of single pores increases with increasing CT content, the overall porosity remains almost unchanged as a result of the suppression of smaller pores in the PVA network with the progressive incorporation of the more homogeneous CT network. Increasing the freezing time in the FT cycles also results in a decrease of porosity, which can be associated with a growth in the crosslinking of the network due to PVA crystallization. The linear viscoelastic moduli measured by oscillatory rheology show a qualitatively comparable frequency-dependent response in all cases, with a moderate reduction with increasing CT content. This is attributed to changes in the structure of the strands of the PVA network.

Quantifying the effect of freeze–thaw on the soil erodibility of gully heads of typical gullies in the Mollisols region of Northeast China

The soil erodibility of gully headwalls is a critical factor influencing gully erosion. In some cold regions, the soil of gully headwalls is subjected to a bidirectional freeze–thaw effect (FT), while the quantification of the influence of FT on the soil erodibility of gully heads is unclear. Therefore, five typical and representative gullies developed in farmlands (GF1 and GF2), along unpaved road (GR), in the woodland (GW) and in stabilized gully bed (GS) were selected to quantify the influence of FT on the soil erodibility of gully heads reflected by five soil erodibility parameters including the K factor (K), soil disintegration rate (SDR), mean weight diameter (MWD), soil shear strength (SS) and saturated soil hydraulic conductivity (SHC). A comprehensive soil erodibility index (CSEI) was constructed by combining the above five soil erodibility parameters. This study revealed that FT significantly affected the five soil erodibility parameters and CSEI, of which the K and SDR increased by 22.7 % and 52.3 %, respectively, but the MWD, SHC and SS decreased by 29.3 %, 30.4 % and 26.1 %, respectively. The change in soil erodibility of the gully heads was closely related to the soil and root properties, of which the contribution of roots to the change in soil erodibility of gully heads was increased by 78.5 % after FT on average. Furthermore, FT significantly increased the CSEI at depths of 0–50 cm in GF1, GF2 and GR, and at depths of 0–80 cm in Gw and GS. FT increased the CSEIs of the five gully heads by 20.1 %-37.3 %, with an average of 26.1 %. Evidently, the organic matter content (OMC), soil texture and temperature dominated the change in the CSEI, of which the extremely low temperature and temperature rangeability during freeze–thaw period exhibited the greatest impact on the soil erodibility of the gully heads.

Time-dependent reliability-based charts to evaluate the structural safety of RC wharf decks exposed to corrosion and freeze-thaw effect

User-friendly time-dependent reliability-based evaluation charts are developed in this research to help practitioners assess the structural safety of existing steel reinforced concrete wharf decks exposed to chloride-induced corrosion and freeze–thaw effect. The research methodology consists of developing a time-dependent reliability-based algorithm using Monte Carlo (MC) simulation, conducting a sensitivity analysis to identify influential parameters that affect the wharf reliability, and calibrating user-friendly evaluation charts. Design examples were provided to demonstrate the use of the evaluation charts for predicting the structural safety of wharves subjected to gravity loads. The margin of error of using the developed charts was found to be less than 2.5% as compared to rigorous time-dependent crude MC simulation.

Weathering Processes and Mechanisms of Low-Grade Metamorphic Rock following Freeze-Thaw Processes

A remarkable risk in the field of rock engineering is the natural exposure of low-grade metamorphic rock to the freeze-thaw process. Examples of such materials are slate and phyllite, which are employed approximately mountainous permafrost zones. In order to study the weathering processes and mechanisms in low-grade metamorphic rock following freeze-thaw weathering processes, the freeze-thaw cycles were applied. Accordingly to this process, low-grade metamorphic rock partially or completely deteriorates, and mechanical properties, microstructure, and mineral content changes are commonly associated with freeze-thaw processes. This study shows that, following numerous freeze-thaw cycles processes, the quality, wave velocity, and compressive strength of rock reduce; calcite, mica, feldspar, and pyrite contents decrease; and clay minerals and gypsum content increase. Furthermore, the study also demonstrated that the changes in quality, wave velocity, and compressive strength caused by weathering of the rock followed the sequence slate > phyllite. However, the mineral contents of slate and phyllite alter in the same way. Because of this increase in volume and subsequent F-T cycles, new cracks form on the surfaces of pores due to outward pressure, and a lot of water is absorbed by clay minerals. The amount of water increases once again due to freezing as the temperature falls below zero degrees Celsius. This course duplicates with cyclic temperature changes and causes deterioration of low-grade metamorphic rock materials. By analysis of an examination of the damage variables based on wave velocity, it is possible to conclude that mineral changes during the freeze-thaw effect may make for the formation of voids and the deterioration of metamorphic rock. This research contributes to a better understanding of weathering processes and mechanisms of low-grade metamorphic rock following freeze-thaw weathering processes.

Resilient modulus of a compacted clay with different moisture and temperature histories

ABSTRACT This paper reports a series of experimental studies to compare the influences of different moisture and temperature histories on the resilient modulus (M R) of a compacted clay. Parallel specimens that were compacted at the optimum moisture content (w opt) were equilibrated to six different moisture contents (w) and subjected to different numbers of freeze–thaw cycles (N FT = 0, 1, 3, 10) before determining the M R and the unconfined compressive strength (UCS). Specimens were brought to each testing condition (i.e. the combination of w and N FT) through two or three different interlaced wetting-drying and freeze–thaw processes. Such a procedure imposed different moisture and temperature histories on the specimens. Experimental results demonstrated that different moisture and temperature histories only result in noticeable differences in the M R for specimens tested at the dry side of the w opt and N FT = 1. The differences become negligible at all w levels after freeze–thaw effects have stabilised at N FT = 10. Different Moisture and temperature histories do not differentiate the relationships of the M R and UCS to the w and N FT. Meanwhile, the relationships of the M R to the UCS are unique and linear regardless of the different moisture and temperature histories.

Bacterial healing of geopolymer concrete exposed to combined sulfate and freeze-thaw effects

In this study, metakaolin-based colemanite and red mud substituted geopolymer concrete were exposed to combined sulfate and freezing-thawing effects to simulate the effects of cold locations with a sulfate environment. Firstly, samples were exposed to a 5% sodium sulfate solution for four days for combined sulfate and freezing-thawing effects. Then, these samples were subjected to freezing-thawing according to TS EN 15177. Finally, cracks formed on the samples exposed to combined sulfate and freeze–thaw effect. Then, the bacterial healing process was applied to heal the cracks. Sporosarcina pasteurii bacteria were used to form CaCO3 in the cracks. The capillary water absorption, weight measurements, splitting tensile strength, ultrasonic pulse velocity, microstructural analyzes, and visual assessment of bacterial-healed geopolymer concrete samples were performed. As a result of this study, the healing ability of Sporosarcina pasteurii was successfully demonstrated by filling cracks caused by the combined durability effect with CaCO3 precipitates. Also, the recovery percentage of splitting tensile strength of the bacterial-healed samples was obtained as 61.71%.

Analysis of Microscopic Pore Characteristics and Macroscopic Energy Evolution of Rock Materials under Freeze-Thaw Cycle Conditions

The repeated cyclic freeze-thaw effect in low-temperature environments causes irreversible damage and deterioration to the microscopic pore structure and macroscopic mechanical properties of a rock. To study the effects of the freeze-thaw cycle on the porosity and mechanical properties, the indoor freeze-thaw cycle test and mechanical tests of sandstone-like materials were conducted. Based on nuclear magnetic resonance, the influence of the freeze-thaw cycle on microscopic pores was analyzed, and the intrinsic relationship between porosity and mechanical strength was discussed. Meanwhile, the energy change in the uniaxial compression test was recorded using the discrete element software (PFC2D). The influence of freeze-thaw cycles on different types of energy was analyzed, and the internal relationship between different energies and freeze-thaw cycles was discussed. The results showed that the microscopic pore structure is dominated by micropores, followed by mesopores and the smallest macropores. With an increase in the freeze-thaw cycle, both micropores and mesopores showed an increasing trend. The porosity showed an exponentially increasing trend with the increase in freeze-thaw cycles. The peak strength and elastic modulus decreased exponentially with the increase in freeze-thaw times, while the peak strain showed an exponentially increasing trend. The strain energy and bond strain energy showed a trend of increasing and decreasing in the front and back stages of the peak strength, respectively. However, the frictional energy always showed an increasing trend. The total energy, strain energy, bond strain energy, and friction energy all showed exponential increases with the increase in the number of freeze-thaw cycles.

Freeze-thaw failure characteristics and strength loss of non-penetrating fractured rock mass with different fracture densities

Rock mass usually contains cracks, joints and other defects with different density and spatial combination characteristics in the diagenetic process. Under the freeze–thaw effect, they continue to expand and connect, which continuously weakens the strength property and poses a serious threat to the stability of rock mass. Previous studies paid more attentions to the strength reduction of rock, failing to directly reflecting the freeze–thaw damage characteristics of rock mass. In this paper, the freeze–thaw failure characteristics and strength loss of non-penetrating fractured rock mass with different fracture densities were studied by means of theoretical derivation and laboratory tests. Firstly, non-penetrating fractured rock mass samples with different fracture conditions were prepared. Then the freeze–thaw samples were subjected to laboratory compression tests and the loss of uniaxial compressive strength was measured. On this basis, the theoretical values of geological strength index GSI was calculated for the samples, and the rough prediction empirical model of GSI for non-penetrating fractured rock mass treated with different freeze–thaw cycles was obtained through data fitting. Finally, by combining the apparent observation method with acoustic emission monitoring technique, the effects of freeze–thaw cycles and fracture density on the failure characteristics of non-penetrating fractured rock mass samples were analyzed comprehensively from both the macro and micro perspectives.

Experimental investigation and finite element analysis on lateral behavior of reinforced concrete columns subjected to freeze-thaw cycles

In cold regions, lateral load-deformation response of reinforced concrete column exposed to outdoor freeze-thaw environments may be significantly deteriorated. In this paper, a method is developed to model the lateral load-deformation response of reinforced concrete column that may experience strength deterioration due to freeze-thaw cycles. The proposed model accounts for uneven distribution of freeze-thaw damage within the cross-section of structural components. The model captures the uneven progression and extent of strength degradation at a given depth in the cross section as a function of number of freeze-thaw cycles. The model is developed using the experimental data from pseudo-static testing of six large scale reinforced concrete columns subjected to freeze-thaw cycles. The column specimens have different concrete strengths and are subjected to different axial loads. An existing model that only considers even distribution of freeze-thaw damage is used to validate the proposed model. Furthermore, the performances of the models are assessed, including monotonic and cyclic responses. Overall, the proposed model can capture the monotonic and cyclic responses of frost-damaged reinforced concrete column relatively well while accuracy is slightly lower for large axial loads. Also, the results reveal an important limitation of the existing even model in modeling freeze-thaw effects.

Effect of freezing-thawing on the quality changes of large yellow croaker treated by low-salt soaking during frozen storage.

The production of the large yellow croaker has seasonal and regional characteristics, which is typically preserved on ice, possibly leading to its deterioration in a short time. Therefore, in this study, we focused on the effect of temperature fluctuation on the quality changes of the large yellow croaker during frozen storage. In this experiment, the large yellow croaker was soaked in a low-salt solution, and physical and chemical properties, water-holding capacity, color, and protein characteristics of the muscle were investigated after repeated freeze-thaw (F-T) cycles and frozen storage. The results show the deterioration of muscle quality of large yellow croaker after low-salt treatment was lower than that of the salt-free soaking group. The salting treatment significantly (P < 0.05) enhanced the yield of large yellow croaker, which was 24.3% greater than the salt-free soaking group after 6 weeks of frozen storage. The microstructure of the salted muscle was more stable and maintained its cellular structure after F-T cycles and frozen storage. The b* value of the salt-free soaking group increased from b* value of the low-salt soaking group decreased from acceptable range. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis indicates the content of 17 kDa peptide decreased in the low-salt soaking group, and the peptides at 21 and 24 kDa increased during frozen storage. The results of the present study provide guidance for the optimal processing, transport, and storage of large yellow croaker, but the effect of salting on lipid oxidation and protein oxidation requires further study.

Linking pore structure characteristics to soil strength and their relationships with detachment rate of disturbed Mollisol by concentrated flow under freeze–thaw effects

In mid-high latitude areas, seasonal freeze–thaw cycles generate significant effects on pore structure of soils, and in turn, affect soil mechanical properties and soil erosion processes. Furthermore, soil particles can be detached on ridged farmland by snowmelt or rainfall concentrated flow due to topographic relief during the spring snowmelt period. To explore the changes in pore structure characteristics under freeze–thaw effects on soil detachment rates under simulating concentrated flow, fifteen soil columns and twenty soil tanks underwent a freeze–thaw pre-treatment of zero, one, five, ten, and fifteen cycles. Soil structure characteristics were quantitatively obtained by scanning soil columns with industrial computer tomography at a 25-μm resolution. Soil strength was measured by a portable vane shear instrument on the surface of soil tanks. Detachment rates of soil tanks were measured in a flume under changeless flow shear stress (τ = 2.32 Pa). Results indicated that freeze–thaw effects significantly decreased soil strength by changing pore network structure, including increasing total imaged porosity and elongated-pore porosity. The detachment rate significantly rose with the rising freeze–thaw cycles (p < 0.05) and had a power relationship with the soil strength (R2 = 0.503, p < 0.05). Thus, the increase in detachment rate was mainly caused by the decrease in soil strength, which is dependent on large and elongated pores that formed during freeze–thaw cycles and on the geometrical characteristics of the pore network. The findings improve the understanding of the generation mechanism of soil erosion as a result of changes in pore structure characteristics during the spring snowmelt period.

Influence of the freeze-thaw effect on the seasonally frozen riverbank stability: A case study of the typical reach of Songhua River, China

岸滩侧蚀崩塌现象普遍存在于江河湖泊中，是一种危害较大的自然灾害。季节性冰冻河流受水动力、冻融耦合作用，岸滩崩塌机理复杂，开展其岸坡稳定性研究对河势控制和河流综合治理具有重要意义。以松花江干流大顶子山航电枢纽下游近坝段为例，采用BSTEM断面尺度模型，对河岸崩塌过程进行了模拟，定量分析了冻融作用对河岸稳定性的影响。研究结果表明：涨水期河岸稳定性相对较高，洪水期和退水期稳定性相对较低，为崩岸多发时期；冻融作用会使河岸稳定安全系数F_s提前达到不稳定临界值，即与不考虑冻融作用相比，河岸提前崩塌，且考虑冻融作用的崩塌宽度更接近实测值，累计冲刷崩塌总量增幅约为7%~41%。研究结果可为季节性冰冻河流岸滩崩塌及河道演变研究提供一定借鉴和参考。;The phenomenon of lateral erosion and collapse of bank is widely distributed in major rivers in the world, which is a kind of natural disaster with great harm. Seasonal frozen rivers are affected by the coupling of hydrodynamics and freeze-thaw, and the mechanism of bank collapse is complex. The research on the collapse process is of great significance to river bank protection and comprehensive river management. Taking the downstream part of the main stream of the Songhua River near the dam of Dadingzishan Aviation Power Project as an example, the BSTEM model was used to analyze the bank slope stability in different periods by considering the freezing and thawing effect, and the collapse process of the dual structure bank was simulated. The results showed that the stability of the river bank was higher in the dry and high water periods, and the stability was lower in the flood period and the receding water period, which was the stage of frequent bank collapse. Considering the freezing and thawing effect, the simulated river bank slope shape and collapse width were in good agreement with the measured values, and the amount of erosion and collapse was increased by 7%-41%. The research results can provide some reference for the study of river bank collapse in seasonally frozen areas.

Water content variation of railway track sub-ballast layer in seasonal frost area: A case study from Finland

Many previous international studies have found a clear relationship between railway track water content and track geometry problems. The proper drainage of substructures is important in ensuring the safe and efficient operation of tracks. This importance will be emphasized in the future with the increasing frequency of extreme weather phenomena and the raising axle weights of train traffic. In many studies, excessive water content has been found to cause excessive geometry deterioration and mud pumping. These problems are usually related to thin substructure layers. However, in this case study, Finland, track substructures are thick due to frost protection requirements and behave differently to thin substructures. In this study, the long-term water content of three instrumented test sites was monitored to study the seasonal and freeze–thaw effects, as well as the effects of drainage improvement made at one site. In a previously reported part of the same research project, the measured water contents were used in an extensive cyclic loading triaxial test series evaluating the loading resistance of substructure materials taken from the same sites. The drainage improvement resulted in a marked decrease in the average water content at the drainage improvement test site. Simultaneously, high momentary water content values also disappeared. The role of capillary water was observed to be less than expected on Finnish railways.

Energy Dissipation and Damage Evolution during Dynamic Fracture of Muddy Siltstones Containing Initial Damage under the Freeze Thaw Effect

This research aims to evaluate the influences of the freeze-thaw (F-T) effect on the energy dissipation mechanism and damage evolution characteristics of muddy siltstones containing initial damage. At first, four initial damage levels were achieved by applying different impact loads to the intact rock, and the damage stresses for levels I, II, III, and IV initial damage were 9.80 Mpa, 17.00 Mpa, 23.34 Mpa, and 32.54 Mpa, respectively. Then dynamic compression tests were conducted on the muddy siltstones containing initial damage after 0, 5, 10, 15, 20, 25, 30, and 40 F-T cycles in the temperature range from -20 to 20 °C. The damage variable of the muddy siltstones was determined by studying energy distribution during fracture of the rock. The damage evolution characteristics of the muddy siltstone containing initial damage under the F-T effect were explored combined with the fractal theory. Test results show that (1) the dynamic compressive strength of the muddy siltstones decreases exponentially with the increasing number of F-T cycles; the dynamic compressive strength of muddy siltstone with different initial damage decreased by 54.9%, 48.4%, 39.4%, 42.5%, and 44.5% after 40 freeze-thaws, respectively, compared with that of intact. (2) The absorbed energy, reflected energy, and transmitted energy of the muddy siltstones subject to different levels of initial damage exhibit step-like changes under the effect of F-T cycles and the rate of decrease in absorbed energy decreases in the late stage of F-T cycles. (3) Both the damage variable and the fractal dimension of the muddy siltstones show an increasing trend with an increase in the number of F-T cycles, and it is more difficult for damage to become superimposed as the damage accumulates to that range causing fatigue (the damage variables ranged from 0.73 to 0.97) while the fractal dimension of the fracture surfaces in the rock still increases. (4) With the gradual increase in the damage variable, the energy absorption density of the rock is negatively correlated with the fractal dimension of the rock fragments.